Conventionally, as a dynamic quantity sensor of the above-described type, a pressure sensor described below has been proposed (see, e.g., Patent Literature 1).
Specifically, in this kind of pressure sensor, one surface of a first substrate is joined to a second substrate. In the first substrate, a depressed portion is provided at a part of another surface opposite to the one surface joined with the second substrate. Thus, a thin portion is formed in the first substrate on one surface corresponding to the depressed portion formed on another surface of the first substrate. In the thin portion, a gauge resistor is disposed, and a resistance value of the gauge resistor changes in accordance with a pressure applied to the gauge resistor. In the second substrate, a recessed portion is formed on one surface joined with the one surface of the first substrate so that the recessed portion faces the depressed portion to form a reference pressure chamber between the second substrate and the first substrate and seals the gauge resistor in the reference pressure chamber.
In the pressure sensor, a film portion which is displaced in accordance with a pressure is provided by the thin portion of the first substrate. When a pressure is applied to the film portion, the film portion is displaced to change the resistance value of the gauge resistor so that an electric signal corresponding to the resistance value is output as a sensor signal.
The manufacturing method of the above-described pressure sensor includes preparing the first substrate to which the gauge resistor is attached, providing the recessed portion in the second substrate, bonding the first and second substrates to each other, and forming the depressed portion in the first substrate.
In the above-described pressure sensor, the relationship between the depressed portion formed in the first substrate and the recessed portion formed in the second substrate is not specifically defined. As a result, a problem arises as the following. When a boundary line (end portion of the thin portion J1a) of the thin portion J1a, which is defined by side walls of the depressed portion J1 and the depressed portion J1, is longer than an open end of the recessed portion J3 as shown in FIG. 10, the film portion J5 is likely to be displaced due to the stress generated when the first substrate J2 and the second substrate J4 are bonded to each other.
In other words, the stress generated when the first and second substrates J2 and J4 are bonded to each other is likely to be concentrated on an end portion of the junction region between the first and second substrates J2 and J4. That is, the stress is likely to be concentrated on the first substrate J2 at a portion where the first substrate is connected to the open end of the recessed portion J3 of the second substrate.
In the above-described configuration, the boundary line between the side walls of the depressed portion J1 and the thin portion J1a is longer than the open end of the recessed portion J3. Thus, the film portion J5, which is displaceable (deformable) in accordance with an applied pressure, is disposed within a part of the thin portion J1a of the first substrate J2 which faces the open end of the recessed portion J3. That is, the film portion J5 is defined by the open end of the recessed portion J3. In other words, the film portion J5 has a length equal to a length of the open end of the recessed portion J3. As a result, the stress generated in the portion of the first substrate J2 which faces to the open end of the recessed portion J3 is applied directly to the film portion J5. Consequently, the film portion J5 is likely to be displaced by the stress, and this kind of displacement may cause fluctuations in output signals.
The above-described pressure having the film portion is described as an example. However, a similar problem also arises in an acceleration sensor or angular velocity sensor having a thin film structure and formed of first and second substrates bonded to each other.